Low-cost, solid-state pressure transducers have greatly improved the medical practitioner's ability to continuously monitor a patient's hemodynamic pressure. In a typical application, a pressure transducer is connected to a patient through an intravascular catheter; its output signal is processed and displayed either digitally in units of pressure, or as a time varying analog trace on a cathode ray tube (CRT) monitor. Once a pressure transducer is connected to monitor a patient's blood pressure, it becomes contaminated and cannot be used with another patient unless sterilized. The medical industry has voiced a clear preference for low-cost pressure transducers that are used with one patient and then discarded. In response, manufacturers have been compelled by competition to further reduce the cost of each new generation of pressure transducer design.
A conventional low-cost pressure transducer typically includes a Wheatstone bridge resistor network deposited on a silicon chip. The resistor network is subject to errors in sensitivity and changes in zero offset caused by temperature effects, which can significantly affect the accuracy of the pressure transducer. Temperature related errors include both those caused by self-heating and errors caused by changes in ambient temperature. Compensation for sensitivity, offset, ambient temperature and self-heating errors have been provided in prior art devices, either integrally on the silicon pressure transducer chip, or on a separate circuit within the pressure transducer housing. An example of the latter type of compensation circuit is disclosed in U.S. Pat. No. 4,576,181.
U.S. Pat. No. 4,557,269, assigned to the same assignee as is the present invention, discloses still another approach to calibrating a disposable pressure transducer. After the pressure transducer is fabricated, it is calibrated to compensate errors in its Wheatstone bridge circuit by trimming a plurality of resistors that are diffused onto a separate semiconductor substrate. Instead of including this semiconductor substrate inside the pressure transducer housing, it is mounted on an external disposable card. The card is plugged into a connector formed on the end of the pressure transducer housing, and stays with the pressure transducer during its use and subsequent disposal. An interface circuit is provided between the pressure transducer and an electromanometry system in which the transducer is used as the pressure sensing element.
While presently available disposable pressure transducers are already relatively inexpensive, there is clearly motivation for reducing their cost even further. The lowest cost, reliable pressure transducer on the market has a significant competitive advantage.
Accordingly, it is an object of the present invention to effect a significant reduction in the cost of disposable pressure transducers without incurring a concomitant decrease in quality. Further, it is an object to reduce the cost of the pressure transducer by including offset, self-heating, and ambient temperature compensation, sensitivity adjustment, and impedance matching in a reusable cable interface that is connected between the disposable pressure transducer and a pressure monitor. These and other objects and advantages of the present invention will be apparent from the attached drawings and the description of the preferred embodiments that follow.